62 



RESEARCHES ON FUNGI 



/ 



24, G). The Pilobolus gun continues to mature (Fig. 12, c), until 

 at last it explodes (Figs. 12, d, and 24, H). When this happens, 

 the gun dies instantly and is thrown backwards on to the sub- 

 stratum of dung, while the projectile, with its freight of living 



spores, travels forward, 

 describes a parabolic 

 trajectory, and lands 

 safely on some object 

 which may be several 

 feet away from the 

 gun which has dis- 

 charged it (Fig. 24, H). 

 As soon as one crop of 

 fruit-bodies becomes 

 exhausted, another be- 

 gins its development 

 (Fig. 24, I-K). 



The Heliotropism 

 of the Pilobolus Gun 

 demonstrated by a 

 Simple Experiment. — 



;x 



■ ■■■v-.'iH'-:--/- / 



Fig. 25. — Result of a simple heliotropic experiment 

 with Pilobolus Kleinii. The fvmgus came up on 

 dung balls spread on the floor of a large dark 

 chamber which was illuminated with daylight 

 solely by a circular glass wall-window one inch in 

 diameter. The photograph here reproduced shows 

 the window and part of the surrounding interior 

 wall, after the end of the experiment. Most of 

 the projectiles hit the window as if it were a 

 target. The local aggregations of the sporangia 

 in the centre of the window were caused by 

 sporangia running together in the drops of cell- 

 sap which were shot on to the glass with the 

 sporangia. Natural size. 



Some fresh dung baUs 

 were spread over the 

 surface of a large cubi- 

 cal culture chamber 

 which was illuminated 

 with daylight solely 

 by means of a circu- 

 lar glass wall-window 

 one inch in diameter. 



After a few days, a number of fruit-bodies of Pilobolus Kleinii 

 appeared on the dung about a foot from the window. The spor- 

 angiophores bent heliotropicaUy toward the source of light and 

 discharged their sporangia at the window. The photograph repro- 

 duced in Fig. 25 shows the window and part of the surrounding 

 interior wall of the chamber at the end of the experiment, after 

 the chamber wall had been illuminated to enable the photograph 



